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David W Evans, Mei-Chuan Margret Yu, Pinakin Gunvant Davey; Luminance and visual acuity: 20/30 could be 20/40!. Invest. Ophthalmol. Vis. Sci. 2019;60(9):5909.
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In a previous study we showed that existing CVA units in different clinics and different examination lanes varied significantly in luminance levels and these devices were also significantly different than newly purchased CVA units. This luminance variation led to significant differences in measured visual acuity in ocular healthy individuals (Evans et al ARVO 2018). Here we extend our research to determine the impact of testing luminance on patients with decreased vision due to various retinal conditions.
Forty-nine eyes of 49 individuals that had known retinal pathology and visual acuity 20/50 to 20/25 on a standardized ETDRS chart, were included in the study. Visual acuity measurements were performed on all subjects by one of two investigators using three clinically representative luminance conditions. The three luminance levels were obtained by adjusting one CVA unit to 40, 79 and 376 cd/m2. The order of presentation of the luminance levels was randomized. The visual acuity thresholds were measured three times, each time with a different set of randomized Sloan letters.
The logMAR acuity values were 0.295, 0.272 and 0.199 for 40, 79, and 376 cd/m2 respectively. The level of luminance significantly influenced measured visual acuity (One-way ANOVA (F=14.57, p=1.73 E-6)). Further, for individual levels of luminance, significant differences existed for measured visual acuity. The visual acuity measured at 40 cd/m2 was significantly different than for 79 and 376 cd/m2 (paired samples t-test, p=.00008, and 8.8E-16). The visual acuity measured at 79 and 376 cd/m2 were also significantly different from each other (paired samples t-test p=1.74 E-13).
Commercially available CVA units vary significantly in luminance, even when comparing existing units and those newly purchased from manufacturers. The measured visual acuity, using strict measurement protocol with three different clinically representative luminance levels, caused a clinically significant variation of one full line of measured visual acuity. The levels of luminance in CVA units is an important clinical variable that can lead to fluctuation in patient measured VA. Testing luminance levels should be standardized with continuous monitoring as they tend to vary between devices and are prone to degradation over time.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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